Deciding on an IP Addressing Format for Your Network

The number of systems that you expect to support affects how you
configure your network. Your organization might require a small network of several dozen standalone
systems that are located on one floor of a single building. Alternatively, you
might need to set up a network with more than 1,000 systems
in several buildings. This setup can require you to further divide your network
into subdivisions that are called subnets.

When you plan your network addressing scheme, consider the following factors:

The type of IP address that you want to use: IPv4 or IPv6

The number of potential systems on your network

The number of systems that are multihomed or routers, which require multiple network interface cards (NICs) with their own individual IP addresses

Whether to use private addresses on your network

Whether to have a DHCP server that manages pools of IPv4 addresses

The worldwide growth of the Internet since 1990 has resulted in a
shortage of available IP addresses. To remedy this situation, the Internet Engineering Task Force
(IETF) has developed a number of IP addressing alternatives.

If your organization has been assigned more than one IP address for your
network or uses subnets, appoint a centralized authority within your organization to assign
network IP addresses. That authority should maintain control of a pool of assigned
network IP addresses, and assign network, subnet, and host addresses as required. To
prevent problems, ensure that duplicate or random network numbers do not exist in
your organization. Types of IP addresses in use today include the following:

IPv4 Addresses

These 32-bit addresses are the original IP addressing format that was designed for
TCP/IP. Originally, IP networks have three classes, A, B, and C. The network number
that is assigned to a network reflects this class designation plus 8 or
more bits to represent a host. Class-based IPv4 addresses require you to configure
a netmask for the network number. Furthermore, to make more addresses available for
systems on the local network, these addresses were often divided into subnets.

Today, IP addresses are referred to as IPv4 addresses. Although you can no longer
obtain class-based IPv4 network numbers from an ISP, many existing networks still have
them. For more information about administering IPv4 addresses, refer to Designing Your IPv4 Addressing Scheme.

IPv4 Addresses in CIDR Format

The IETF has developed Classless Inter-Domain Routing (CIDR) addresses as a short to
medium term fix for the shortage of IPv4 addresses. In addition, CIDR format
was designed as a remedy to the lack of capacity of the
global Internet routing tables. An IPv4 address with CIDR notation is 32 bits
in length and has the same dotted decimal format. However, CIDR adds a
prefix designation after the rightmost byte to define the network portion of the IPv4
address. For more information, refer to Designing Your CIDR IPv4 Addressing Scheme.

DHCP Addresses

The Dynamic Host Configuration Protocol (DHCP) protocol enables a system to receive configuration
information from a DHCP server, including an IP address, as part of the
booting process. DHCP servers maintain pools of IP address from which to
assign addresses to DHCP clients. A site that uses DHCP can use a
smaller pool of IP addresses than would be needed if all clients
were assigned a permanent IP address. You can set up the DHCP
service to manage your site's IP addresses, or a portion of the addresses.
For more information, refer to Chapter 12, About DHCP (Overview).

IPv6 Addresses

The IETF has deployed 128–bit IPv6 addresses as the long term solution to
the shortage of available IPv4 addresses. IPv6 addresses provide greater address space than
is available with IPv4. Oracle Solaris supports IPv4 and IPv6 addressing on the
same host, through the use of dual-stack TCP/IP. As with IPv4 addresses in
CIDR format, IPv6 addresses have no notion of network classes or netmasks. As
in CIDR, IPv6 addresses use prefixes to designate the portion of the address
that defines the site's network. For an introduction to IPv6, refer to IPv6 Addressing Overview.

Private Addresses and Documentation Prefixes

The IANA has reserved a block of IPv4 addresses and an IPv6
site prefix for use on private networks. You can deploy these addresses on
systems within an enterprise network but be aware that packets with private addresses
cannot be routed across the Internet. For more information on private addresses, refer to
Using Private IPv4 Addresses.

Note - Private IPv4 addresses are also reserved for documentation purposes. The examples in this
book use private IPv4 addresses and the reserved IPv6 documentation prefix.